A novel strategy of "waste treating waste" has been implemented in this work. Copper/carbon (Cu/C) composites prepared by the carbonization of waste printed circuit boards (PCBs) were used for the degradation of Acid Orange 7 (AO7). Catalytic degradation of AO7 was conducted by varying carbonization temperatures, catalyst dosage, H2O2 dosage, AO7 concentration, pH values, and anions. Ultrasound significantly improved AO7 degradation, obtaining 93.27% degradation within 90 min. We report that Cu/C composites show good catalytic activity in a broad pH range. Cu/C catalysts were characterized by multitechniques. Cu-0 was the main active component for the generation of center dot OH that was the reactive oxidant for AO7 degradation. The plausible pathway and catalytic mechanism for AO7 degradation were proposed. The unique structure of Cu/C composites gave a combined mechanism of adsorption and catalysis. Cu/C composites showed superior durability for AO7 degradation. Using Cu/C composites as catalysts provides a green approach for wastewater treatment and waste management. (c) 2019 American Institute of Chemical Engineers AIChE J, 65: 1234-1244, 2019